Influence of fiber fusion on loss and beam quality in multi-mode injection conditions

Abstract

A simple model based on coupledmode theory to describe mode evolution and fiber fusion loss at the fusion splicing point is presented. Using the model, the simulations of fundamental mode loss and total power loss, as well as beam quality evolution generated by the fusion interface under different deviation including offset and tilt, are performed for matched and unmatched fiber splicing. In the simulations we consider three states: minimum total power loss state, minimum fundamental mode loss state, and best beam quality state. From the simulations, some interesting results, such as the fact that with certain fusion offset, the output beam quality will be improved and the ratio of fundamental mode will increase, are predicted. In addition, some references for good beam quality as well as low total power loss fusion employing a balance between axial offset and tilt during the actual fusion splice process are provided.

The influence of axial offset of fusion splicing on a large mode area fiber based oscillator

“…The main reason for this is that most of the high order modes excited by Point 2 will be directly emitted from the OC, rather than take part in the gain competition. However, the axial offset has little influence on the optical efficiency in these two cases because the total loss of all the supported modes induced by the axial offset is low [4].…”

“…When the input laser passes through the deviated splicing point, modes in the output fiber are excited by the input laser and each mode in the input laser can contribute to each excited mode in the output fiber. The amplitude of the jth mode in the output fiber excited by the ith mode in the input fiber is [4]:…”

“…(∆x 1 , ∆y 1 ) and (∆x 2 , ∆y 2 ) are the axial offsets at HR FBG and OC, respectively. Each time the laser in the cavity passes through the splicing point, it experiences two mode couplings with deviation of (∆x, ∆y) and (−∆x, −∆y), so the actual mode coupling coefficient in the laser cavity is the product of K c (∆x, ∆y) and K c (−∆x, −∆y), which can be calculated by equations ( 1)-( 4) combined with the mode distribution [4]. It should be noted that the incident optical field that is used to calculate the two coupling coefficient is different due to the reflection of the FBGs.…”

“…Compared to spatial-structure lasers with separated optical components, fiber lasers with all-fiber structure are more compact. However, fiber fusion splicing is an important issue in all-fiber laser systems, due to its influence on optical efficiency and beam quality [2][3][4][5][6]. The splicing quality of the * Author to whom any correspondence should be addressed.…”

“…In 2013, the same group studied the influence of the fusion point on the beam quality based on the beam propagation method [3]. Recently, Zeng et al provided a model to calculate the optical loss and beam quality at the fusion splicing point [4]. The effects of the splicing point on laser output power and beam quality have been studied experimentally and theoretically, however, the influence on fiber oscillators is rarely researched.…”